1. Field of the Invention
The present invention relates to an automatic transmission.
2. Description of Related Art
An automatic transmission generally comprises a torque converter and a transmission gear mechanism. The torque converter is accommodated in a converter casing and the transmission gear mechanism is accommodated in a transmission casing, and the converter casing is arranged integrally with the transmission casing. The transmission gear mechanism is usually operated hydraulically, that is, its friction elements for switching power transmission pathways, such as clutches, brakes and so on, are driven by hydraulic actuators.
The transmission gear mechanism is provided with hydraulic circuits for regulating operation of the actuators. The hydraulic circuits are provided with a variety of devices including select valves and shift valves for switching speed ranges, and some devices contain accumulators. If such select valves or shift valves would be coupled at a rapid timing, a so-called select shock or transmission shock is likely to arise so that a hydraulic supply passage for each actuator for driving the friction element is designed to prevent such rapid coupling of the friction element by means of the accumulator.
The oil passages and various devices for the hydraulic circuits are usually mounted in valve bodies and, in these states, mounted in a oil pan of the transmission gear mechanism. If the accumulators are to be mounted integrally in the valve bodies, however, the oil pan and the casing for accommodating the accumulators are rendered proportionally large because the accumulators are considerably bulky and large in number.
In order to solve such problem, Japanese Patent Early Publication (Kokai) No. 211,920/1983 proposes that the accumulators are separated from the valve bodies and arranged in a transmission casing in a series extending parallel to the axis of the transmission gear mechanism. The separation of the accumulators from the valve bodies provides a high freedom of arrangement of the accumulators and permits a compact size of the valve bodies, thus enabling the automatic transmission as a whole to be minimized to a considerable extent.
In the prior art automatic transmission, however, some of the accumulators arranged parallel to the axis of the automatic transmission gear mechanism are to be arranged at a periphery of the transmission gear mechanism, thus expanding in a direction substantially perpendicular to the axis of the automatic transmission.